1. Field of the Invention
The present invention relates generally to communications receivers, and particularly to a signal detection technique for enabling a receiver to detect desired signals in the presence of jammers or other interferers.
2. Discussion of the Known Art
The rapid growth of modern weapons systems, along with systems used for intelligence and communications, has greatly increased the need for reliable access to the electromagnetic spectrum when carrying out tactical operations. Many sophisticated wireless military communications and jamming systems have recently been disclosed. See, e.g., R. A. Poisel, Modern Communications Jamming Principles and Techniques, Artech House (2004); and O. Holt, Technology survey: Sampling of communications jammers, J. Electronic Defense (February 2008) at pages 43-46, all relevant contents of which are incorporated by reference.
In tactical situations where a number of different radio-frequency (RF) communications systems must be densely deployed, avoidance or reduction of interference among the various systems is paramount if each system is to perform reliably. Enabling the systems to overcome impairments typically caused by spectrum congestion is therefore very important. One known technique being developed for efficient spectrum usage is Dynamic Spectrum Access (DSA) as described in A. N. Mody, et al, Recent advances in cognitive communications, IEEE Comm. Mag., vol. 45, no. 10 (October 2007) at pages 54-61, which are incorporated by reference. Radios using DSA operate to detect, track, and predict the occupancy bands of a potential interferer in time, frequency and space. The radios then shift their operating frequencies accordingly in order to avoid interference.
In certain tactical operations, it is desirable that a blue force “(friendly”) communications system allow soldiers and other friendly users to communicate in the presence of a blue force or friendly jammer that may be operating nearby, for example, to avoid detonation of improvised explosive devices (IEDs) by red force (enemy) cell phones or other wireless devices in enemy hands. The system may be multiplexed with respect to the jammer in time, frequency or space, or other known cancellation techniques may be used to mitigate any adverse effects of the jammer on reception of communications signals by friendly users. See U.S. patent application Ser. No. 12/719,974 filed Mar. 9, 2010, titled “Tactical Radio and Radio Network with Electronic Countermeasures”, which issued as U.S. Pat. No. 8,301,075 on Oct. 30, 2012, and is assigned to the assignee of the present application, and is incorporated by reference.
A need remains, however, for a signal processing technique that will enable a receiver or radio to detect desired communications signals in the presence of an interferer without shifting the frequency or timing of the communications signals, or implementing other cancellation techniques that require a high degree of processing power in the receiver.